Ag/MoO₃–Pd-mediated gasochromic reaction: An efficient dual-mode photoelectrochemical and photothermal immunoassay

Herein, we presented a dual-readout gasochromic immunosensing platform for accurate and sensitive detection of carcinoembryonic antigen (CEA) based on Ag-doped/Pd nanoparticles loaded MoO₃ nanorods (Ag/MoO₃–Pd). Initially, the presence of analyte CEA would prompt the formation of sandwich-type immunoreaction, accompanied by the introduction of Pt NPs labeled on detection antibody. Upon the addition of NH₃BH₃, the product hydrogen (H₂) will interact with Ag/MoO₃–Pd as a bridge between the sensing interface and the biological assembly platform. Both photocurrent and temperature signals can serve as readouts due to the significantly increased PEC performance and enhanced photothermal conversion capability of H–Ag/MoO₃–Pd (the product of Ag/MoO₃–Pd react with H₂) compared to Ag/MoO₃–Pd. In addition, the DFT results show that the band gap of Ag/MoO₃–Pd becomes narrower after the reaction with H₂, thus improving the utilization of light, which theoretically explains the internal mechanism of gas sensing reaction. Under optimal conditions, the designed immunosensing platform showed good sensitivity for CEA detection with the limit of detection (LOD) of 26 pg mL⁻¹ (photoelectrochemical mode) and 98 pg mL⁻¹ (photothermal mode). This work not only presents the possible reaction mechanism of Ag/MoO₃–Pd and H₂, but also creatively applicate it in photothermal biosensors that give a new path for devising dual-readout immunosensor.